Search found 517 matches

by 1024MAK
18 Apr 2019 23:33
Forum: NEW HARDWARE
Topic: System test rom/Board
Replies: 5
Views: 23

Re: System test rom/Board

Wow! That was quick work Martin :shock:

Excellent progress and excellent work 8-) :D 👏

Mark
by 1024MAK
13 Apr 2019 23:53
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 51
Views: 245

Re: Resurrecting an MTX500.

Assuming it was the +5V that was shorted out, the most likely item in the power supply section of the board that will have been damaged is the current boost transistor, Q4 (TIP2955). That’s the large power device on the heatsink. Also check it’s the associated resistor (R62, 10 ohms) and the 7805 vo...
by 1024MAK
12 Apr 2019 15:14
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 51
Views: 245

Re: Resurrecting an MTX500.

There should be enough room at the rear of the case, next to the video board riser, possibly above the video RAM to fit a board with a PLCC socket. Other than the data lines from 4000-05/06 ROM A socket it shouldn't need many from the other two should it? Data and address lines are all the same for...
by 1024MAK
12 Apr 2019 15:10
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 51
Views: 245

Re: Resurrecting an MTX500.

Also you will find this old post of mine useful. Although please don’t reply in that thread until I have sorted out the missing photos in the last post...

Mark
by 1024MAK
12 Apr 2019 15:04
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 51
Views: 245

Re: Resurrecting an MTX500.

Electrically it is easy to replace each ROM chip with EPROM or EEPROM/flash ROM chip if the only requirement is to only allow read access. The problem is a one of a mechanical / size nature as some of the signals are on different pins and mask ROM chips have a lower pin count compared to the equival...
by 1024MAK
12 Apr 2019 11:33
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 51
Views: 245

Re: Resurrecting an MTX500.

For 5V TTL based systems like the MTX, logic low is 0V to 0.8V. Logic high is 2V to 5V. Anything inbetween is undefined and not valid. More info here . If all the data bus lines float to such a value, you can add either ‘pull-up’ resistors (to +5V) or ‘pull-down’ resistors (to 0V). Each data line sh...
by 1024MAK
12 Apr 2019 00:12
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 51
Views: 245

Re: Resurrecting an MTX500.

If you adapt the PCB (cut some tracks and add some modification wires) it is possible to use EPROMs. But first, try removing all the ROM chips and see what happens to the data bus. If all the data bus lines float to logic high, the Z80 will execute RST 38h repeatedly. If all the data bus lines float...
by 1024MAK
10 Apr 2019 19:36
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 51
Views: 245

Re: Resurrecting an MTX500.

The edge-connector details are in the Memotech BASIC Tutor Reference and Operators Manual / Memotech Operator's Manual (on one of the pages that has the schematic diagrams) and also in the MTX 500/512 Service Manual and Technical Information manual (PDF page 23, paper page 20). Does that give all t...
by 1024MAK
10 Apr 2019 15:33
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 51
Views: 245

Re: Resurrecting an MTX500.

The edge-connector details are in the Memotech BASIC Tutor Reference and Operators Manual / Memotech Operator's Manual (on one of the pages that has the schematic diagrams) and also in the MTX 500/512 Service Manual and Technical Information manual (PDF page 23, paper page 20). Visit Dave’s web site...
by 1024MAK
10 Apr 2019 13:50
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 51
Views: 245

Re: Resurrecting an MTX500.

The /RESET line should go low then high again if the two keyboard reset keys are both pressed together and then released. Or if the keyboard is disconnected, short the relevant pin on the keyboard connector (on the main board) to 0V briefly. If you have a breadboard and some suitable 74xxx series lo...